Two chamber reaction furnace

ABSTRACT

A vertical two chamber reaction furnace. The furnace comprises a lower chamber having an independently operable first heating means for heating the lower chamber and a gas inlet means for admitting a gas to create an ambient atmosphere, and an upper chamber disposed above the lower chamber and having an independently operable second heating means for heating the upper chamber. Disposed between the lower chamber and the upper chamber is a vapor permeable diffusion partition. The upper chamber has a conveyor means for conveying a reactant there through. Of particular importance is the thallinating of long-length thallium-barium-calcium-copper oxide (TBCCO) or barium-calcium-copper oxide (BCCO) precursor tapes or wires conveyed through the upper chamber to thereby effectuate the deposition of vaporized thallium (being so vaporized as the first reactant in the lower chamber at a temperature between about 700° and 800° C.) on TBCCO or BCCO tape or wire (the second reactant) at its simultaneous annealing temperature in the upper chamber of about 800° to 950° C. to thereby replace thallium oxide lost from TBCCO tape or wire because of the high annealing temperature or to deposit thallium on BCCO tape or wire. Continuously moving the tape or wire provides a single-step process that effectuates production of long-length TBCCO superconducting product.

BACKGROUND OF THE INVENTION

The United States Government has rights in this invention under ContractNo. DE AC36-83CH10093 between the United States Department of Energy andthe National Renewable Energy Laboratory, a division of the MidwestResearch Institute.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates in general to a furnace in which chemicalor physical reactions occur, and in particular to a two chamber reactionfurnace wherein the chambers are disposed substantially vertically inrelation to each other and the temperature of each chamber thereof canbe individually controlled, with the chambers being separated from eachother by a vapor-permeable partition to thereby permit interactionbetween reactants situated in different chambers. Also included ismethodology for the interaction of reactants.

II. Description of the Prior Art

In certain chemical and physical reactions between one or morereactants, it is not unusual for reactants to require two or moredifferent temperatures, all above ambient, for steps of a reaction toproceed. When this is the case, current single-chamber, and thereforesingle-temperature, furnaces require multi-step procedures to accomplishcomplete reactions. Such multi-step procedures can include heating afirst reactant at a given temperature for an appropriate time period ina furnace, and thereafter either increasing or decreasing the furnacetemperature before adding a second reactant to the furnace for a secondperiod of time. As is apparent, such a multi-step process is bothinconvenient, time-consuming, and energy inefficient while additionallyrequiring invasion of the furnace chamber when reactants areincompletely reacted.

Current two-zone furnaces having a first temperature zone and a secondtemperature zone in horizontal relationship to each other permitvaporization of a material in one zone and vapor travel to the secondzone for subsequent deposition thereof. However, one major drawback ofhorizontal zones is that vapor deposition is not uniform, but instead agradient of deposition quantity occurs as the vapor travels horizontallythrough the second temperature zone.

Exemplification of a process wherein reactants thereof require differentactivation temperatures in order to yield the required end product isfound in the manufacture of thallium-barium-calcium-copper oxide (TBCCO)substrates having superconducting properties. In particular, a TBCCOsubstrate is first annealed at temperatures of about 800° to 900° C., atwhich temperature thallium is highly volatile and can be lost from thesubstrate. Accordingly, an external source of thallium is usually neededto compensate for any thallium loss. In a single-chamber, fixedtemperature furnace, this external source is usually vaporized thalliumderived from a thallium source identical to the composition of theend-product to be produced. The thallium source is heated to atemperature between about 700° and 800° C., thus about 100° less thanthe annealing temperature. In a single-chamber furnace, the initialTBCCO reactant is therefore annealed first at the higher temperature.Thereafter, at the lower temperature, the initial TBCCO reactant isexposed to thallium vapor which is normally combined with an oxygenbackground pressure and flow. Simultaneous annealing and thalliumreplacement thus cannot occur in a single-chamber furnace to produce thefinal TBCCO substrate end-product. Employment of a two-zone horizontalfurnace permits simultaneous vaporization and deposition, but, asearlier noted, creates a deposition gradient and resultantnon-uniformity of desired end-product.

In view of the above, it is evident that a need is present for atwo-chamber furnace where reactants therein can simultaneously reactuniformly to completion when different temperature values are requiredfor respective reactants. Therefore, a primary object of the presentinvention is to provide a two-chamber reaction furnace wherein thechambers are situated substantially vertically in relation to each otherand wherein the temperature of each chamber can be individuallycontrolled.

Another object of the present invention is to provide a vertical twochamber furnace wherein the chambers are separated from each other by avapor-permeable partition to thereby permit interaction betweenreactants situated in different chambers and at different temperatures.

Yet another object of the present invention is to provide methodologyfor producing a product wherein a first reactant thereof requires afirst temperature while a second reactant thereof whose vapor is to bedeposited on the first reactant is so vaporized simultaneously at asecond temperature.

These and other objects of the present invention will become apparentthroughout the description of the invention which now follows.

SUMMARY OF THE INVENTION

The present invention is a vertical two chamber reaction furnace. Thefurnace comprises a lower chamber having an independently operable firstheating means for heating the lower chamber and a gas inlet means foradmitting a gas to create an ambient atmosphere, and an upper chamberdisposed above the lower chamber and having an independently operablesecond heating means for heating the upper chamber. Disposed between thelower chamber and the upper chamber is a vapor permeable diffusionpartition. In a preferred embodiment each chamber has a respectivesupport means for supporting a respective reactant situatable thereon.Additionally, the upper chamber can have a conveyor means for conveyinga reactant from a first location outside of the furnace through theupper chamber of the furnace to a second location outside of thefurnace.

The present invention additionally comprises a process for depositing avaporizable first reactant on a second reactant wherein the vaporizablefirst reactant volatilizes at a first temperature and deposition of thatfirst reactant on the second reactant occurs simultaneously at a secondtemperature. The process comprises providing a vertical two chamberfurnace as defined above and placing a vaporizable first reactant withinthe lower chamber and placing a second reactant within the upperchamber. The lower chamber is heated to a temperature sufficient tovaporize the vaporizable reactant within the lower chamber whileadmitting oxygen and/or an inert gas as required to effectuate suchvaporization, with vapor thereof passing through the partition into theupper chamber. The upper chamber is heated to a temperature sufficientto react the second reactant while the vaporized reactant passes throughthe partition and is deposited simultaneously on the second reactantwithin the upper chamber. Of particular importance is the thallinatingof long-length TBCCO precursor tapes or wires, which can bethallium-free (e.g. barium-calcium-copper oxide BCCO!) or can containthallium (e.g. TBCCO), conveyed through the upper chamber via theconveyor means to thereby effectuate the deposition of vaporizedthallium (being so vaporized as the first reactant in the lower chamberat a temperature between about 700° and 800° C.) on TBCCO tape or wire(the second reactant) at its simultaneous annealing temperature in theupper chamber of about 800° to 950° C. to thereby replace thallium oxidelost from the initial second reactant because of the high annealingtemperature. Compounds of other metals, such as the substitution of Sr,Pb and Bi for the Tl, Ba and Ca of TBCCO for example, can, of course,change the reaction temperature. In the substitution example given, thereaction temperature is higher. The tape or wire is continuously movedby the conveyor means to yield a single-step process that effectuatesproduction of long-length TBCCO superconducting product.

BRIEF DESCRIPTION OF THE DRAWINGS

An illustrative and presently preferred embodiment of the invention isshown in the accompanying drawings in which:

FIG. 1 is a front elevation view schematically in section of a twochamber furnace; and

FIG. 2 is an end elevation view along line 2--2 of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, a furnace 10 is shown schematically. Thefurnace 10 has a lower chamber 12 and an upper chamber 14, with theupper chamber 14 disposed above the lower chamber 12. The wall 16 of thefurnace 10 is constructed of tubular stainless steel and is openable atits top 18. Disposed between the two chambers 12, 14 is a vaporpermeable partition 20 here constructed of baffles which function toadmit vapor from a reactant in the lower chamber 12 to pass into theupper chamber 14. A typical exhaust stack 38 is provided.

Disposed within the lower chamber 12 is a fixed platform 22 whichfunctions as a first support means upon which a first reactant can besituated. A gas inlet 48 enters the lower chamber 12, and has aplurality of dispersion nozzles 50 therein to permit entry of a gas asdesired to create a specific ambient atmosphere depending upon therequirements of the reactant(s) there present. Access to the lowerchamber 12 can be accomplished through an access port 40 located inalignment with the platform 22. Disposed within the upper chamber 14 isa second support means which can be a fixed platform or, as here shown,a conveyor means including a conveyor belt 24 for conveying a secondreactant such as a length of tape 26 from a first location 28 outside ofthe furnace 10 through the upper chamber 14 to a second location 29outside of the furnace 10. Access to the upper chamber 14 for both theconveyor belt 24 and the second reactant thereon is through respectivebaffles 42, 44 having respective gas blankets and situated through ductcomponents of the exhaust stack 38. Movement of the conveyor belt 24 isaccomplished by conventional means such as a motor powered byelectricity. Respective ceramic heating elements 30, here being "Globar"elements manufactured by Cesiwid Company, Niagara Falls, N.Y., aredisposed near both the first and second support means to thereby providerespective isothermal reaction regions within which the reactants resideduring reaction events. These Globar elements can be sheathed withaluminum oxide to minimize any degradation thereof which may occur in acorrosive environment.

Operation of the furnace 10 is exemplified in the preparation of acontinuous length of TBCCO tape, as described below.

Example

The respective heating elements 30 in both the lower chamber 12 andupper chamber 14 of the furnace 10 were activated to heat the lowerchamber 12 to a temperature of between about 700° and 800° C. and toheat the upper chamber 14 to a temperature between about 800° and 950°C. An alumina boat 46 housing thallium oxide 52 was placed within thelower chamber 12 on the platform 22 within the isothermal reactionregion, and oxygen gas was admitted through the gas inlet 48 anddispersion nozzles 50 to thereby provide partial pressure control forthe thallium and oxygen within the lower chamber 12. A length of TBCCOor BCCO tape 26 was placed on the conveyor belt 24 at a first location28 and was thereafter conveyed into (and subsequently through) theisothermal reaction region of the upper chamber 14. The TBCCO or BCCOtape 26 was annealed in the upper chamber 14 at the set temperature of800° to 900° C., with a portion of the thallium of the tape 26 beinglost therefrom because of the high annealing temperature.Simultaneously, the thallium oxide 52 within the alumina boat 46situated in the lower chamber 12 was vaporizing, and the vapor therefrompassed through the vapor permeable partition 20 into the upper chamber14 to effectively replace or maintain the initial thallium lost from theTBCCO tape or to incorporate thallium on the BCCO tape and therebyproduce a TBCCO tape having the required thallium value for efficacy.After a reaction time of one to 60 minutes, depending on the filmthickness desired, the segment of tape 26 so reacted passes onward to afinal destination outside the furnace 10 at the second location 29. Inthis manner an operator can effectuate the thallinating of long-lengthprecursor tape or wire to produce a uniform superconducting productquickly and efficiently because of annealing of precursor tape or wireand simultaneous thallium deposition thereon accomplishable in thevertical two chamber furnace 10.

While an illustrative and presently preferred embodiment of theinvention has been described in detail herein, it is to be understoodthat the inventive concepts may be otherwise variously embodied andemployed and that the appended claims are intended to be construed toinclude such variations except insofar as limited by the prior art.

I claim:
 1. A process for simultaneously replacing a vaporizablereactant that has been lost from a length of reactant during annealingin a reaction furnace wherein a vaporizable first reactant volatilizesat a first temperature and simultaneously replaces loss reactant of alength of a second reactant at a second temperature, comprising:a)providing a substantially vertical two chamber reaction furnacecomprising a lower chamber having an independently operable firstheating means for heating the lower chamber and a gas inlet means foradmitting a gas to create an ambient atmosphere, an upper chamber havingan independently operable second heating means for heating the upperchamber, and a vapor permeable diffusion partition disposed between thelower chamber and the upper chamber, said upper chamber disposed abovethe lower chamber; b) placing a vaporizable first reactant within thelower chamber; c) placing a length of second reluctant within the upperchamber; d) heating the lower chamber to a temperature of from about700° C. to about 800° C. sufficient to vaporize the vaporizable firstreactant within the lower chamber while admitting a gas through the gasinlet means to effectuate vaporization with vapor thereof passingthrough the partition into the upper chamber; and e) simultaneouslyheating the upper chamber to a temperature of from about 800° C. toabout 950° C. to anneal the length of said second reactant and cause aloss of a portion of the second reactant while simultaneously vaporizingthe reactant of (d) on the length of the annealed second reactant toreplace said portion of loss second reactant within the upper chamber.2. A process as claimed in claim 1 wherein a first support means isdisposed within the lower chamber and the vaporizable reactant issituated thereon.
 3. A process as claimed in claim 1 wherein a secondsupport means is disposed within the upper chamber and the length ofsaid annealed second reactant is situated thereon.
 4. A process asclaimed in claim 2 wherein a second support means is disposed within theupper chamber and the length of said annealed second reactant issituated thereon.
 5. A process as claimed in claim 3 wherein the secondsupport means comprises conveyor means for conveying the length ofsecond reactant from a first location outside of the furnace through theupper chamber of the furnace to a second location outside of thefurnace.
 6. A process as claimed in claim 4 wherein the second supportmeans comprises a conveyor means for conveying the length of secondreactant from a first location outside of the furnace through the upperchamber of the furnace to a second location outside of the furnace.
 7. Aprocess as claimed in claim 6 wherein the vaporizable first reactant isTl₂ O₃ and the length of second reactant isthallium-barium-calcium-copper oxide.
 8. A process as claimed in claim 7wherein oxygen gas is admitted into said lower chamber heated to atemperature of from about 700° C. to about 800° C.
 9. A process asclaimed in claim 6 wherein the vaporizable reactant is Tl₂ O₃ and thesubstrate is barium-calcium-copper oxide.
 10. A process as claimed inclaim 9 wherein oxygen gas is admitted into said lower chamber heated toa temperature of from about 700° C. to about 800° C.